Small molecule natural products, primarily of microbial origin, have been extensively used as therapeutic agents for decades. Most searches to identify and characterize such compounds have been dominated either by efforts that seek activities that inhibit microbial growth (antibiotics) or simply by the chemical identification of microbial products without any defined knowledge of their biological function. In recent years, we have begun to recognize that many microbial products serve as signals sensed by diverse microbes as part of the way they adapt to their environment. Based on this ecological perspective of the role of natural products we have developed our central hypothesis: Bacteria synthesize and secrete a large number of small signaling molecules that affect the physiology of other microbes that occupy the same habitat. While this is the general hypothesis driving the proposed research, the lines of experimentation we propose are also discovery-driven: we aim to discover new small molecules that mediate diverse interspecies interactions in the microbial world. The expectation is that by identifying and characterizing such molecules, and studying their biosynthetic pathways and biological functions, we will generate a collection of potential lead compounds. These could eventually be developed as therapeutic agents, either as antibiotics to treat bacterial infections or, as several other natural products currently in clinical use demonstrate, to alleviate other afflictions. To address the question of signaling compounds synthesized by bacteria in a way that will lead to the discovery of many such molecules we have devised approaches that meld the disciplines of microbial ecology, physiology, and genetics, with enzymology, bioinformatics, and small molecule chemistry. In this multidisciplinary manner we will undertake three specific aims: (1) Prospecting for novel microbial signaling molecules, (2) Genome mining by metabolite stimulation, and (3) Characterization of new small molecules: biosynthesis and biological activity. Relevance to public health: The development of antibiotics as therapeutics is one of the key accomplishments of modern medicine. Unfortunately, the appearance of antibiotic resistant bacteria has diminished the effectiveness of existing antiobiotics. The proposed research aims at discovering new antibiotics and other agents with therapeutic potential.